[Vuejs]-How can I tell Vue where my backend is when accesing through network IP instead of localhost?

Yes you are correct. You need to set your api url as the IP address in your vue app i.e. 192.168.1.38:80/api/...
you could potentially use some javascript to check if your on a mobile device and change the url dynamically but the IP i believe should work both on local and from the mobile device