The DC to DC converter listed does not require a battery. I used that for four days camping, and will start again once the weather cools.
Once you start dealing with no batteries, I wonder how the phone deals with surging throughout the day. I put that together with a 12 - 24 VDC USB charger, which may take the panel straight, but I put a DC to DC voltage converter to hold the voltage steady. That way if the DC to DC converter failed, the USB still regulates the power from the panel.
A 10 watt panel like linked could charge it, but with using the phone 24/7 as a wi-if router, I’m not sure if it would charge it enough. I find my phone uses 1 amp (12 watts) when charging, and after charged charged drops to .2 amps - ,3 amps if I’m using it. I don’t know how that would do throughout the night. The 100 watt panel you have would provide charging power throughout all but the cloudiest days.
It’s just figuring out how much energy you need to last through the worst cloudy stretch of days for the year or the shortest winter days.