One of the new mechanics introduced to Fortnite in Chapter 2 Season 7 are the new payphones. These can be found all over the map, and interacting with them will give you access to quests and bounties.
With the number of NPCs on the map in Chapter 2 Season 7 being reduced, the payphones were brought in to ensure that players could also get another bounty or quest. The reward for completing them is an important resource called Gold Bars that players need to buy certain resources, upgrade weapons, and get Exotic weapons.
For the most part, the payphones will appear as part of a bus stop in different locations all over the island. They will often have a red toolbox, gas canister, or ammo box spawn near them. When you get close to one, a small icon will appear on the screen showing you where it is.
To accept a quest or bounty, all you need to do is interact with the payphone, then use the radial menu to select which quest you want to complete. After that, all you need to do is meet the requirements for whatever the quest is, and it will automatically complete.
The value of Gold Bars for the reward will be automatically added to your total and you can then use them on whatever takes your fancy.