>I thought it was risky to leave a phone plugged in all the time
I have had phones on a charging dock for long periods. No issues.
Unless you have some budget small brand phone that was too cheap to be true, most phones are fine plugged in.
I left my ~$1k OnePlus phone on the wireless charger for after ATT told me I couldn't use it and forced their spyware Samsung phone on me, The battery puffed up after about a year.
It's a statistical thing. Most phones don't explode their batteries. When you have a hundred or a thousand together, the chance that at least one has a battery explosion starts to reach concerning levels and you ask what you can do to avoid it.