Looks like you want to change the mysite Host location to new web application(portal.company.com) and in this process you have to perform two things.

 1. update your user profile services for mysite host location, Create Managed Path, enable self services site creation, 
 2. Now move all existing MySite collection from existing web app to new webApp.

**To move Site collections**

You can detach the database from existing(my.company.com) web application and reattach to portal.company.com web app.

Or u can take the backup of Site collections(My Site) one by one and restore it to portal web app.


helpful http://amjadk.wordpress.com/2012/12/22/mysites-and-the-mysite-host-in-sharepoint-2013/