What am I doing wrong with this Coelogyne tomentosa
 

I've had this guy for three years now and zero spikes. It has probably quadrupled in size in that time period, but it just continues putting out new growth instead of spikes (it's doing so right now). This is the only coelogyne I've ever had so maybe I'm doing something wrong.

Here's what I'm doing: I have it potted in a terra cotta pot that has several holes and the media is mostly river stones and large bark beneath and sphagnum on top. Why river stones? To be honest, it came potted that way and since I didn't know anything about it, I just followed suit when I repotted. I keep it under a panel of 4 HO T5s at about 40-70% RH, 60-70F over the winter and then I put it outside in the summer where it gets hot and humid. It is definitely getting good light, sitting alongside cattleyas that bloom consistently. I water it around twice a week on average. I basically try to water it whenever the sphag on top gets dry--it has reacted very positively to this. Ever since I started just letting it sit in a water occasionally like its dendrochilum cousin, it has grown even bigger. It's always putting out adorable red roots. It seems so happy! What does it want to bloom??

Looking at the pseudobulb size differential, maybe it wasn't big enough yet?

I thought so too, but some of the largest growths are from last year so I thought it should be at the point of blooming at this point. I have tried to do research on this plant, and some people suggest they grow very large, but I see a lot of photos of blooming plants that are smaller than this. I was wondering if I'm doing something like not giving it a winter rest or cold temps to induce blooming. Seems there are both warm and cold growing coelogynes, but again I don't have any experience with them. I have one dendrochilum that I got at the same time, and that one was tiny to start out with but blooms about twice a year. I did not know what I was doing with it either, and it seems fine!

Coelogynes.com may help. I haven't grown this one but the ones I have now are much improved over previous yrs as my care of them has also improved. Lovely genus.

I did look on that site, but there wasn't really anything specific about the tomentosa on there, the page on it just describes the blooms, which doesn't help me much. Maybe there isn't any way to trigger blooming in this plant. I keep seeing that it's an easy plant... and it has been easy to grow. I had a paph like this, it grew prolifically, but it didn't bloom for four years until I left it outside until temps dipped below 40F. Now it's finally producing a spike. So I'm trying to make sure I don't waste 4 years on this plant not doing the correct thing.

I have one the same size as yours and it has bloomed at least three times already since I got it as a single pbulb.
The main difference from yours is the potting technique (medium included). They like to be on the moist side so large bark and stones, together with a terracota pot might not be very good.
I use plastic pots with a mix of medium size bark+LECA+cork chips+perlite.
I would sugest a repot with a slightly more water retentive medium+pot. Now it's the time to do it as they are about to start the growing season.

About the light...I'm not sure about the equivalence of your overhead lights to natural conditions. My plant is near a very large and bright window, it doesn't get any sun, only bright light...but there's a catch, this bright light is from a north faced and unobstructed window.

Thank you! This is so helpful. I did notice it seems to like when I water it a ton. I often let it sit in water and it will absorb it over a day like a phrag. It has exploded since I started doing that. I've heard they hate repotting, but I think it's sounds like the place to start. Maybe the prior owner used the stones because they won't degrade, making repots less regularly needed? I think I will try something with more sphagnum, which I use for more of my thirsty plants because I'm something of an underwaterer.

I think the equivalent of the light I'm giving it is higher than yours, so I am going to rule that out. Before I put it under lights, I had it in a very bright eastern facing bay window where cattleyas regularly bloom and grow vigorously. It's sitting next to a cattleya under the lights that's putting a spike out right now. I also put it outside for about 4 months of the year.

What kind of temps do you keep yours in? I've found that temperature is usually the culprit for me when it comes to getting some stubborn plants to bloom.

In winter between 15ºC and 22ºC (these are only the boundaries but it doesn't follow a rule. Sometimes when there's no sun and I'm out to work, temp is 15ºC. When I get home and turn the A/C on at night, it will be 22ºC.
When there's sun, it's 22ºC but at night, when I go to sleep, it goes down to 15ºC).
In summer, it get a little hard for it as it is between 24 and 28ºC consistently, which is too much but, so far, it has handling it nicely (more water is the key under these conditions). Your temps seem to be ok.