Cell Phones & Tube Amps

I have, for many years, avoided plugging my cell into tube amps. I occasionally used my laptop as a source, but never the cell.

But recently I moved the charger near the tube amp, so I figured why not try it? It was convenient, easy, and gave me access to a wealth of music, even if I wasn't using a fancy DAC as part of the chain. The volume was limited, but some YouTubes and digital feeds actually sounded half-decent.

But after 10 or 20 minutes, the cell would jam up with a locked display, either a bright white screen or horizontal stripes, and the only way to fix it was to take it apart and remove and re-insert the battery. After it happened a few times, I tried to figure out what was causing this.

It seemed like the charging had something to do with it, so I ended up reversing the plug on the charger, since it didn't have a polarized plug with a fat prong that could only be plugged in one way. It seems to have fixed the problem. 

Are there any reasons that a cell shouldn't be plugged in to a tube amp? Can I damage the phone or the amp?

Perhaps it's better to use a USB dac or something like a Dragonfly. I don't really want to go Bluetooth. 
I can't seem to edit that title. The ampersand is messing it up.
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I'm not sure I understand your comment. Are you saying that the cell is not a good enough source?
I think you have just answered your own question.
We run cell phones into tube amps all the time with no worries.

But it does sound like there is a problem here. Its not a tube thing so much as a 'this specific amp' thing.
I think it was a polarity issue. It didn't hurt the amps, but it sure shut down the phone. These are old amps, Leak TL12+ monoblocks and one plugs into the other. None of the plugs are polarized.

I think flipping the plug on the charger fixed it, because it hasn't happened since. And it didn't do it with the charger disconnected. I'm listening to it now and McCoy Tyner sounds pretty good at 720k. The bass and cymbals aren't up to par, though.