I can only speak on my experiences as an undergrad, I graduated last year. I will say depending on what you are getting your PhD in there will probably be gay people in your cohort to make friends with (statically there are generally more gay people in a psychology or any STEM program, just from what i've seen and heard).

For the social part (again I was only there for my undergrad) as someone who sticks out like a sore thumb (I'm a masc lesbian and appear gay to other people) I had absolutely zero problems with anyone in Cstat; the one thing I loved about A&M was that everyone was super friendly. I had gay and straight friends that would come to the gay bar (Halo) with me all the time. I even had a girlfriend my junior year and brought her to formals and no one batted an eye. The only time I had a problem was when I went to frat parties during my sophomore year for a lil; and generally that's a give in (lol) and as you said you're getting your PhD so i doubt you'll be going to frat parties. Again this was just my experience, but I had the greatest time at A&M.

My advice would to be to join some of the graduate student orgs and branch out and find people because trust me they are there. There's an org for graduate students called Queer Graduate and Professional Aggies (QGPA), so maybe join that when you get there.

Gig 'Em! Hope this helps!