Most modern smartphones use cryptography to prevent others from accessing information on the phone. This includes when a phone is 'on' but 'locked' and an adversary has physical unrestricted access to the phone.

If someone has access to a modern laptop computer that is booted, but the screen is locked, an adversary with unrestricted physical access to the device can be assumed to be able to compromise your data (unless protected by additional layers of encryption) fairy trivially