You can keep using your old phone, but no updates means no security updates. This means your browser and other apps are susceptible to compromise. As time goe

You can keep using your old phone, but no updates means no security updates. This means your browser and other apps are susceptible to compromise. As time goes on the exploits are automated, this becomes less the provenance of determined organizations, and more accessible to script kiddies or casual hackers. If the drivers are open source you can at least run something like LineageOS or another Android derived open source ROM and still run an updated OS on your old hardware.