I think the only way to minimize the risk is to create a user profile that you use when you're at risk of your phone being stolen (e.g. outdoors). If your phone is snatched, only that profile will be unlocked and the other profiles will be locked.
You could also think about physical protection like a case with a cord attached to your wrist or bag (like a miniature kensington lock), which would give you more time to react before your phone is snatched.