Which is more economical with resources, an e-tick or a paper ticket?
According to this study by the IATA, it costs \$1 to process an e-ticket, versus \$10 to process paper ticket. I assume this is only from the airline's point of view. You could argue that this is not the "environmental cost" you care about, but I just wanted to point it out.

I'm a bit confused by your phone charging assumptions, but according to this post, it costs close to 1 cent to charge a phone (10,000 mAh, at least). Also, you won't need your phone at full charge to use e-ticket.

On top of that, paper tickets also have a lot of costs associated with it, from the manufacturing process, logistics of getting the paper to your local store, getting it from the store to your home. Then we need to talk about recycling costs, etc.

So without the cost of the phone taken into account, I still think it's more efficient to use e-ticket.