Oh my god I found it…
I knew it was gonna be stupid.
put_resp_cookie(conn, key, value, opts \\ [])
Options
:domain- the domain the cookie applies to:max_age- the cookie max-age, in seconds. Providing a value for this option will set both the max-age and expires cookie attributes:path- the path the cookie applies to:http_only- when false, the cookie is accessible beyond http:secure- if the cookie must be sent only over https. Defaults to true when the connection is https:extra- string to append to cookie. Use this to take advantage of non-standard cookie attributes.
I had :secure forced to true but I’m not using HTTPS in my dev environment.
I hope this discussion will help others determine how they want to implement token authentification with Phoenix and Vue.js 
Thank you all again for your time and support <3
