Someone has gone thru my cellphone without permission and checked my messages. is this legal?

is it legal for someone to pick up my cellphone and go through my messages without my permission?
Update: the phone was in a common place in breakroom w all other phones on table. mine was locked & 2 bosses and another employee unlocked it (generic code) and went thru my text messages. They proceeded to call someone that I had texted but hung up when someone walked in on them. What do you think?
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