If a phone gets stolen, you can easily file a complaint, get that sim deactivated and a replacement within an hour. Put it in another phone and logout of any accounts from the stolen phone. If the stolen phone has a lock, then it is pretty difficult for a random thief to extract the data from the phone.

Source: My phone was stolen in 2014 and had my brother’s phone number in it who was in another country. My parents lodged a complaint the next day, deactivated the sim and got a replacement in 3 hours. My phone didn’t have a lock but thankfully I did not have any sensitive data on it and I reset my google account password ASAP after I lost it and logged out of all devices. I still use all the important accounts that were on that phone till this date.