How can I put telephone participants (that have dialed-in) into breakout rooms?

How do I move a telephone participant to a breakout room?   I tried and they stay in the main room with "(not joined)" next to their phone number.   The steps I'm following are:   After creating a breakout room with the option assign manually (have also tried assign automatically), then assign the participant to the room, and Open All Rooms, a message pops up the the participant has been invited to join the breakout room.   How does the participant join?  They're not prompted to take any action to join, just silence.   Preferably, how do I put them in the breakout room without them having to do anything?    Thank you.