Agree that this is probably best, maybe combined with a time condition (if you have a regular bed time!).
Something to note with iPhones- you can’t scan a tag for home assistant and have it auto-execute your automation. It prompts that a tag has been scanned and then asks if you want to open home assistant…at which point just make a Lovelace button to toggle your automation as you’ll have to interact with your phone! There are hacky work arounds (last time I checked) with the shortcuts app to bypass this, but at that point maybe just use the mobile app sensors!
As an addition after re-reading your post requirement for multiple chargers, if you had a cheap smart plug on each charger, you could measure the current draw and use that as a condition for different automation actions (combined with the mobile app charging state sensor). That way you could identify which charger your phone was placed upon.