To elaborate a bit on @mladen’s answer, your phone wouldn’t be compliant with PureOS, and you don’t want (yet) PureOS on your phone.
First, your phone’s driver probably are not free and/or not supported by the average linux (and PureOS, which is based on debian). Under these conditions, it is quite hard to fit a Linux distribution on your phone.
Second, PureOS is made for the desktop at the moment. Purism’s hard work and efforts will make it mobile friendly in the coming year. If you want a Linux (non-Android) replacement for your phone, Plasma Mobile seems to be your best bet. Although it’s not suitable for daily use.