A solar charger that'll fit on a bar bag won't keep a smart phone continually charged. Take one much bigger than that and a lot of sunlight. Your best, most practical bet, is a hub generator. Or a rechargeable ancillary battery pack that you can plug in somewhere at night and then use to boost your phone during the day.

I guess the Brunton in the link might do the job when AC recharged. It is basically a rechargeable battery pack.

Maybe what we need is this, referenced in the current solar charging thread. Powerful, and priced right.