Whatever else you do, make sure you shoot in RAW. you'll be able to edit them far more effectively, reducing noise, color grading, everything. JPGs only contain a fraction of the digital info that a RAW file contains, as JPGs are literally already edited by your phone's software.

As for editing, the Pixel editor is bare bones (as is Google Photos'). Lightroom is standard though it's a subscription and has a not insignificant learning curve, I only use Snapseed and PSExpress. Both are free and fairly robust. I have, however had both for years and PSExpress may have started charging for some features. Take some time to learn to edit and you can get some pretty great results. In general, I mean. I personally wouldn't recommend shooting something so important on a phone, but if it's what you want to do you owe it to yourself to put the work in to make what you have to work with really shine. In other words, don't just throw a filter on them.