If your dad was doing his best he would try to understand you. As Jot-Aro Kujo said, it would be a good idea to talk to other adults if it is safe for you, so that they talk to your dad. I know it is scary to be open about who you are and who do you want to be. As well as you, I also uncome out to my parents a few times because I felt pressured to be someone I am not, and that feels like shit. If it is hard for you to talk face-to-face with your dad, you could try to write him a card explaining ALL your feelings. If he thinks this is a phase, you could say something like 'even if it is a phase (and I don't think so), I need you to support me, and to try to understand me'.
I hope things get better soon, good luck.