Just an idea, not a complete solution:
Samsung has 7 letters, the pin is also 7 digits long.
So there could be some mapping between each of the letters of Samsung and the pin.
Also, 6 looks a big like a capital G.
The two S in Samsung map to different digits. So if my first assumption is correct, it is not a straight substitution and you have to take into account something else, for example the position of the letter in the word. Or the difference could be because the first S is uppercase while the second is lowercase, and those would be considered different in this mapping.
EDIT after the hint, still not solved:
I assume by "the Samsung lock screen" it means the one where you can enter a PIN. To me it seems like a standard phone keyboard where several letters are mapped to a digit. I can't see the connection yet, though.
If we try to spell "Samsung" using the phone digits it would be 7267864. It's interesting that "Samsung" this way ends with "864" and the PIN starts with "438". Which is almost the same in reverse, but I it could just be a coincidence.
It is also interesting that all the digits of the PIN are different, and include everything from 1 to 6, but then skip 7 and go straight to 8.
It is also interesting that the penultimate digit is 1, which doesn't map to any letters. So we can consider it as a space. I thought the PIN can match the phone's model, but it seems that all Samsung phones are "Galaxy (something)" which poses two problems - Galaxy is 6 letters long, if we then include a space and the letter for the model, it doesn't fit the PIN.