Where are you going? Domestic or international? Destination?

Also, does your employer require refundable fares?

IIRC Egencia is a corporate travel agent and corporate travel management service with most bookings done through their website. Thus there is probably a small fee for UA to take over a ticket. In addition, you should check whether upgrading violates company policy since it usually involves reissuing the ticket, so that technically you're refunding the ticket and no longer traveling on the ticket your employer provided. Some companies don't like this while a few others just forbid premium cabin travel by employees on business trips.

Depending on the destination and routing, your corporate travel agent could issue tickets under codeshare numbers or on ticket stock other than UA. Either one can be an issue when you try to use miles or money to get an upgrade.