Invasion of Privacy?

So, I am going to tell you about something that happened at work today. I work as a lifeguard/swim instructor at a local pool, and I have great coworkers and annoying bosses (like everyone, right?)

Anyways, we have a rule about no cell phones out while at work, which is no big deal. So, yesterday, one of my coworkers was leaving and took out his cell phone to check his messages as he walked out. However, he got distracted on his way out, and he left the phone on the staff table. An hour later, another one of my coworkers found the phone, but as we didn't know what to do with it, we just left it on the staff table.

A few hours later, the guy who lost the phone called and asked if anyone had seen it. We said we saw it, but when we looked at the staff table, it was gone.

So, today, the guy who lost his phone asked my boss if she had seen it, and she said that a parent had turned it in. We all know this is a lie because we were there when it was found, and it was not a parent who turned it in. Also, what parent would take something off the staff table? No, clearly, my boss found the phone and nabbed it.

Ok, so my boss is lieing about finding the phone, that should be no big deal. However, things get worse. Apparently, my boss went through my coworker's texts and phone calls to see if he had every texted during work. I don't know what evidence she found, but today my coworker was put on probation based on evidence found on his phone.

So, what I want to know is if this is an invasion of privacy? I know that legally, the cops wouldn't be allowed to peruse his phone without a warrant, so is my boss allowed to? Does the fact that it was left on the pool deck give her the right to violate his privacy? Why is she not being truthful about how she found the phone? Why is she such a bitch?

I know that personally, I would never want anyone going through my texts. I text to Sally (who knows I am gay) about being gay, and if someone found that, it would be a really bad situation. Of course, I delete most of the texts that could be incriminating, but I may have forgotten one. I think that my boss was way out of line in going through his texts, and if I were him, I'd threaten a law suit against her.