"并肩同行" can be translated as "to walk side by side" or "to walk together" in Engpsh. Here are some examples of how you might use these phrases in a sentence:

We walked side by side down the street, enjoying the warm weather and each other's company.
The two friends walked together, chatting and catching up on old times.

Both of these phrases convey the idea of walking alongside someone, either as a companion or in sopdarity.