Have I done this? Yes
Have famous authors done this? Yes
Is it okay to do this? To a point

So you're reading a story and you get to something like this:

"Are you okay?" I asked the man. "What's your name?"

"Imma doin' fine. Jerst Fauntastic. Me name's Old Man Jimm-ay. Ya 'r a little shert fur yer age aren't ye? What be yer own name?"

I don't even know what that was, I just don't like it.

Everyone has an accent. Your accent sounds normal because that's how you have been speaking for your entire life. When I go to read a book, yes, I know people have different accents, but writing things that people with different accents say phonetically just leaves me confused.

Now depending on the character, this could work. If the accent is drastically different, ex. Hagrid from Harry Potter, you could lightly drizzle in some phonetics and make it work. But most of the time this because a hassle to read and downright offensive. I don't want to read a book with someone of my accent and have phonetics completely messing up the sounds.

Now I get slang. Like y'all and other slang from that area is perfectly fine to use, and can even help with characterization... as long as that isn't overboard as well.

So you may be wondering, "How on Endor am I supposed to write like this and still have the reader know about the accent?" That's as simple as writing, "In his heavy Scottish accent he said, 'My name is Jimmy.'" The reader most likely knows what a Scottish accent sounds like, and can use that prior knowledge to piece together what the accent would sound like. The reader is happy and manages to unconsciously do all of the phonetic work themselves and you get to not have to do the extra work to add those phonetics. It's a win win situation.

Good luck!
-Ellie