Do u think whether using apostrophe is formal or not ?
Apostrophes are used in contractions, and that makes the writing informal.
He can't win the game because he didn't practice enough.
To be formal, it is better to write:
He cannot win the game, because he did not practice enough.
Apostrophes are ALSO used to show possession:
He knows Bob's guitar belongs to Bob, because the guitar was in Bob's room with his other possessions.
WHEN AN APOSTROPHE IS USED TO SHOW POSSESSION, it is
not informal.
...has broadened phone users' minds by offering...---- this is not informal.
:-)