Confidentiality – Does the saying "physical access = game over" also apply to smartphones?

I was surprised to read in the answers to the popular question that it is almost impossible to secure a computer system if the intruders have physical access.

Does this also apply to smartphones? Suppose I did everything I could to secure my phone at the software level (for example, encrypted storage, restricted application permissions … whatever you consider to be "maximum secure"). Is physical access still terminated?

This seems to be a significant issue, as there are many situations in the daily life of most people where they leave their cell phone on their desk while they take a break or what have you.

Technical responses are welcome, but I would personally appreciate the readable responses to a person with no experience in information security.

This question is related, but it concerns more the surveillance technologies that could be integrated into a smartphone, not the options available for a malignant person with physical access.