you need a better DC charger for your phone then... I have several cigar plug chargers that are dual 2.1A USB, and others that are USB C 3 amp. these charge my Pixel just as fast as my wall plug chargers
I do carry a '400W' portable inverter that I try to never pull more than 200W out of, and have used it to charge computers and so forth that don't have 12V supplies, I try to only use it when the sun is shining, and most of those laptops have like 65-90W PSU's. this small inverter only draws max 10 watts more than the output load, so its quite efficient. I installed a 'powerpole' DC outlet fused at 30A to power this inverter (12V at 30A is 360 watts).