<human>: Can you succinctly summarize the text in 1-3 sentences?

Background knowledge for you all- I am in a serious 2 year relationship with a man and we have been doing the long distance (300 miles) since we began dating. 

My boyfriend attends physical therapy 3x weekly. He has a male physical therapist, and he has been going to him for about 10 months now and they have become somewhat friends. There is a female PT there too. Well, I noticed on twitter they were going back and forth with inside joke tweets, which, at first, irritated me a bit. I shared my thoughts and feelings about the issue, and he responded with some defensive comment, along the lines of "Oh it's nothing. Relax" and then tried to explain to me what he said meant. I have dropped it and that is that. I also forgot to mention my boyfriend is very personable and friendly. I don't think he has bad intentions but sometimes he comes off as flirtatious. I saw under his phone contacts her name listed. (I believe the female PT has a boyfriend as well). My question is, should I be mad? Should I bring up the issue? As I mentioned above, he is personable and very friendly. Does that still make it ok to get her number? My real question for him is WHY did he get it?? WHY did he need it? Should I tell him it's wrong or should I drop it and pretend I never saw it? I would appreciate advice from both males and females! Preferably if you are in a serious relationship as you may be able to relate a bit more :) THANK YOU!
<bot>: Serious BF has the phone number of a female physical therapist in his phone from where he goes to therapy. It is not his therapist. Do I acknowledge this issue or pretend I never saw it? Should I be mad?