In case you have not seen the root cause, Jack Dorsey's "hacked" Twitter posts were generated through Tweets appearing to come from his phone number: Forbes: Twitter Blames Mobile Provider 'Oversight' For Hack On Jack Dorsey's Account.
Use of phone number as a vector attack is on the rise. In case you have not read about it, SIM jacking has been a threat recently. You can find interesting tips to protect against such threat and react in case your have been hijacked here: The SIM Swapping Bible: What To Do When SIM-Swapping Happens To You.