In English, "上飞机" is typically translated as "to board a plane" or "to get on a plane." The phrase comes from the verb "to board," which means to get onto a vehicle or vessel, such as a train, ship, or airplane. Here are some examples of sentences using this phrase:

I need to get to the airport early so I have time to board the plane.

The flight attendants will make an announcement when it's time to board the plane.

Please make sure you have your boarding pass and passport ready before boarding the plane.

We boarded the plane and found our seats.