It's recommended to use Android Open Source Project (AOSP) ROMs to be sure there are no spyware on your phone, good ROM's are:
Since AOSP comes without Google Apps by default, it means it has no Play store.
https://f-droid.org is a great alternative as an app store for fully open source software. It includes applications such as
Shelter to isolate untrusted apps from your personal data
Firefox Klar for privacy browsing
K-9 mail client
Linphone for SIP communications
OpenVPN client
Revolution IRC client
ownCloud,
Nextcloud clients
NewPipe a YouTube client
Yalp store,
Aurora store for downloading apps from Play Store without Google account
MaterialFBook for accessing Facebook without its official app,
Tinfoil for TwitterTelegram FOSS build,
Silence for encrypted SMS chats
Delta Chat for encrypted secure instant messaging over email (has a Telegram-like interface and group chats)
orBot as a Tor client ( thanks to
https://guardianproject.info )
among a big variety of other privacy-oriented apps.
Open GApps is a fully open source Google Apps alternative.