@babybear1129,
Once a cheater, always a cheater.
Being pregnant isn't easy, but it won't get any easier if you're always worrying about the actions of your boyfriend. This can lead to stress which is really not good for the baby or for yourself. I wouldn't be able to be strong either if my boyfriend was doing the same; you are not alone.
Love yourself first. If your boyfriend won't respect you enough to love only you, you shouldn't be with him. I know that everyone has their own level of insecurities, but if your gut is telling you that he's acting suspicious with his phone, he probably is up to no good. We are wired as humans to be able to sniff out cheaters and liars. Don't lie to yourself because you are blinded by your current love. It may or may not get any better even after the baby arrives.
Sorry if I went on a ramble or if my response even helps you at all. I just really dislike cheaters and it made me angry. I wish you all the best and I hope you find out what's best for yourself and the baby.