Is it possible to open a car's door lock with smartphone?

Cars typically do not use IR to unlock - they use radio waves instead. So this won't work.

However, attackers have been successfully using versions of this attack which uses RF, for quite some time now.

In the early days, the attacker would use RF jamming to stop your keyfob locking the car. Simple, but reasonably effective against folks who wouldn't check their car was locked.

Not long after that attackers moved to recording the RF signal and replaying it - so manufacturers developed systems that would not respond to a replay attack, and instead would require a new code to be transmitted each time.

A current attack is a relay attack - where they get the code from your key which is inside your house and transmitting it directly to a device held next to your car. See this carlock.co article for more info.