nkglider,buddy, Please do not suspect your wife ever unless you have some concrete convincing proof! If you suspect her then her every action, every move will become suspicious to you! See friend woman does not gives in so easily!
Sometime back i have read an article regardind the symptoms of cheating spouse Do not know weather they will help you or not However i am telling you !
1) If the spouse is cheating he/she does not leaves mobile phone unattended !Even while going to wash/ bath room they carry it with them and they do not exchange their cellphone or reluctant to exchange even if need arises(On this count she comes true as she left her phone with you as she thought she had nothing to hide)
2) Second symptom that was given was such(cheating) spouses while on computer immediately minimises the page they have been working on when someone gets close to them!
I know both of these are lame and rubbish kind of symptoms but anyhow this was what given
Again i will tell you that do not suspect your wife have a faith on her!
Regarding her FB friends and those things please do not try to see any untoward things out of nothing!