Im using Laravel 5.3 in Homestead with Vagrant 1.8.7 running on VirtualBox.
I have need to enable some php extensions.
I know that I could ssh into the box and
you should first log onto Homestead server using ssh ( probably you know this already - "vagrant ssh").
then go to "/etc/php/7.0/fpm/" there is also for cli on this location "/etc/php/7.0/cli/" edit it with "sudo vi php.ini" ( esc and :wq to save changes ).
then you should restart nginx: "sudo nginx -s reload"
and after that, restart php-fpm: "sudo service php7.0-fpm restart"
if you are not sure if it is php 5.x or 7.x on your homestead, use "find / -name php.ini" to find php.ini, you will probably get 2 or 3 results.