Hi Alex,
The plastic jar will indeed be waterproof, but not likely UV resistant. A glass jar should fair better (but not necessarily the lid). Some PVC plumbing pipe + end caps of any size greater than the phone is better. Leave some holes in the bottom cap, and cover with flyscreen, etc - for ventilation. The phone will cook in a sealed container. Perhaps hacksaw 15cm worth off someone's downpipes...
...Preferably with their permission - lest you wish to test your ability to "reason you way out of any conflict" ~ Mirko.
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