One technical term to describe the altering of rhythm in a musical phrase is agogic or (agogic accents). Another example of bringing out a rhythmic quality would be a delaying of a particular note in a phrase to heighten the suspense of what follows it.
With any Art, the artist accentuates certain qualities, colors, forms, aspects of the work to expressively communicate ideas or feelings. In music, this is done with dynamics, tone colors and pitch but also with rhythm!
*Important: There is a limited range in which you can exaggerate the rhythm otherwise you'll start messing with the pulse too much. To bring out a rhythmic characteristic of the musical phrase, you must be tasteful so don't overdo pushing the momentum or holding the tempo back too long or too often. As Steven Isserlis once said, "If in doubt, stay in tempo!"
How do you learn rhythmic expression? Sing! And then try to sing like that with your cello bow. Also, listen to great musicians and notice how their rhythm flows. Does it sound like a computer could have played it - probably not - so what is different?
