Re: As you might expect...
"Unless someone turns off both GPS and the phone system it will always be able to triangulate you and so it is impossible to get truly lost."
There is one other scenario, in which your phone's battery runs out. Which is why taking a paper map & a compass as backup is sound advice.
BTW don't get me started* on how shit google maps and their alternatives are. White roads with grey edges on a pale grey background doesn't make for readable mapping, especially on a phone in broad daylight. OS is the gold standard to which all other maps should aspire.
* Looks like I did that myself. I'll get me gore-tex jacket.