Outlook working with Exchange and POP3 emails

[TripleNut]

I have a Dell laptop running Windows 7 Pro #32. It was originally a home-only PC but it now gets used at work on a domain. I am running Outlook 2007 which was originally just for POP3 private email. At work we have Microsoft Exchange Server and Outlook now picks up both sets of email and they both seem to run OK side by side within the same version of Outlook although it won't send POP3 from work, only home, no biggy. The issue I have is that the POP3 emails are private and Exchange emails are for work. This arrangement seemed fine and I assumed they would remain separate i.e. POP3's stay on the laptop and Exchange emails are stored on server. That is until I setup my new smartphone to download Exchange (work) emails. This worked fine and downloaded work (Exchange) emails but it also downloaded my private POP3 emails which leads me to think that actually ALL my emails are now sat on the work server. This can't be allowed to happen.

Would really appreciate some input on whether this assumption is correct. If it is, is there a way to separate them out in the same version of Outlook and also where on the server will copies of my private emails be kept as I'd like to remove them?