A Flight Attendant reported they could not communicate with the flight deck due to inoperative handsets after the aircraft suddenly stopped while taxiing to avoid another aircraft.

Narrative

FA (Flight Attendant) #2 handset stopped working during boarding; not able to use to call any cabin; unable to make PA or call flight deck. Maintenance placarded inoperative. During taxi immediately following the demo as the cabin crew was checking for compliance the Captain SLAMMED on the brakes to avoid another aircraft. All FAs went flying toward the aft with the exception of the #1 who was making her PA and was slammed into the galley. We received NO phone call from the flight deck to ask if we were ok. I could not have contacted them if I was injured due to the INOP interphone. This was an unsafe situation to be put in while at work. There was also no concern from the flight deck over the sudden stop that threw us all into seatbacks. There was a jumpseater and they may have been distracted. Suggestions: FA handset should NEVER be placarded. Should be a no-go item for the FAs safety. Cockpit crew members should be concerned for their Cabin Crew when a sudden and extreme braking situation occurs.