TravelonWomen's Anti-Theft-Class Small East/West Crossbody Bag

Q: Will a large phone (~3.5" x 6.8" with case) fit in the phone pocket?

Yes, a large phone will fit in the phone pocket. I carry the iPhone 6 in the pocket.

Q: Is there room for a 16 oz (or smaller) water bottle?

Yes. It’s deceptively roomy. It would easily hold a 12-16 ounce water bottle

Q: So is this a safe bag to take to a workplace with no personal area? Will i need actual locks?

This just makes it so when walking no one can easily open purse to grab wallet. The wallet section has the anti theft, so cards can't be scanned when walking by. The clips on these keep the zippers from opening and strap can't be cut. I really can say about your work area, this just helps so your personal information can't be scanned, stolen while traveling