Google offers free unlimited storage for their Pixel phones. No need for additional off-phone storage, however you CAN insert a usb-C flash drive into your Pixel phone and manually transfer them if you choose.
Being able to transfer pictures from your Google Pixel 3a is a great option to have. You can certainly transfer photos from the Google Pixel 3a to a flash drive by following the steps provided at https://www.verizonwireless.com/support/knowledge-base-224323/. RobertC_VZW
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