Have you had a look at using https://developer.mozilla.org/en-US/docs/Web/API/Geolocation_API ? @Colin's suggestion makes use of this in the mobile device browser, which you can send back to a host/cloud-based node-red instance via web-sockets, or a pub/sub protocol like mqtt.
If you want to build a new node, check out node-red-contrib-web-components as a basis -- it might help to make it straightforward to wrap the browser geolocation data into server-side node-red events
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