Of course, happy to help! You might say, "May I reach you at the number you're calling from?" Or "Would it be convenient for me to return your call at the number you're currently dialing from?" These politely convey your intention to return their call to the same number.

Can I call you back on this number? Can I use this number to call you back on?

These days many customer service reps are asking, "Is this a good number to reach you at?" or "Is [reads back number] the best number to reach you?"

Why not avoid complications and just use the number itself? "May I call you back at [number]?"