How can I view photos stored on my computer from my Pixel phone?

For access from outside your home, a NAS or a small home server is another route. You could keep the photos on it and connect securely using something like Tailscale rather than exposing the folders directly to the public internet. It costs more and takes more setup, so cloud syncing or a local network share is probably easier to start with.

You can share the photo folders on your computer over your home network and use an Android file manager that supports SMB or Windows network shares. This lets your phone browse the files without uploading them anywhere, but it generally only works while both devices are on the same Wi-Fi network. Make sure the shared folders are read-only if possible and use a strong computer password.

The simplest option is a cloud-sync service. Install Google Drive or OneDrive on the computer and sync your existing photo folder. The files can remain on the computer while also being available through the service’s phone app, and they won’t use phone storage unless you download them. Keep your external-drive backups too, since syncing is not the same as a backup.