I dont think its suspicious...so far. I'm friends with a few of my exes on fb. Its nothing suspect, we have all moved on, i occasionally speak to them- how lifes going etc. It is nothing untoward. But saying that, mine are all exes from a long time ago, if the exes are more recent and she is speaking to them then i would be a little concerned.
As for looking at her phone and not telling you...so what? If i receive a text while im with my bf, i will sometimes look at it and then put my phone down, not saying anything to my bf about it...if he asked i would tell him (though would be wondering why he asked in the first place) I dont have to report back to him about every interaction i have with other people- that would be unreasonable. However, her turning her phone off could be seen as suspicious.
Life is not measured by the number of breaths we take, but by the moments that take our breath away.