Well all I need to know is if it’s against company policy to walk up to someone else’s car and ask them out on a date! Would I still be employed afterwards??
Jesus! I’m glad this is slightly entertaining to most of you
To the best of my knowledge mixing work and play is not against any specific policy (unless it crosses into harassment or the two(or more) involved are in positions that could benefit or harm the position of another involved in the relationship. That being said the old saw "don't

where you eat" comes into play. What some of the folks here are saying is while it's technically fine, it's most likely gonna bite you in the ass in the end.
Search of a persons phone is very difficult for even police to get authorization for- much less UPS management. If they want to fire an employee for refusing to unlock their phone to locate messages that may or may not be there- that would be impressively dumb and I would pay money to witness them try to explain that to a union steward. If you are of equal "rank" to the person who owns the phone in question, you can ask, but if you tell them what you are looking for, they will most likely simply tell you to piss off either directly or indirectly. If you don't tell them, I reckon that would end much worse for you.