Chrome browser closed after receving a call
This is probably because of the amount of RAM on the device you are using. It sounds like the system gave the RAM that was being used by Chrome to the phone app. It saw that Chrome was no longer the active app and the phone app was requesting more RAM so in order to free up the RAM it had to close Chrome.

If Chrome was using a majority of the system RAM, and a new app requested access to the RAM, the system needed to free some up. 

Since you did not specify what device you have though, this is really only a guess.