Fedora runs natively php 7.2
And even if i ran ./configure --with-lsphp7 , it still installed lsphp5 and now i am compiling lsphp7 from OLS admin (works beautifully).
But it would be nice if "--with-lsphp7" worked out of scratch.
--with-lsphp7 is just a name, equipped with a default experimental very small lsphp5.6 binary which can not be used for any applicaiton, you will still need to install lsphp binary through compiling yourself( for Fedora 28) or rpm installation for CentOS systems or package installation for Debian/Ubuntu systems.
If remi PHP repo works on Fedora 28(not sure, and never test it), you can use it as well. remi has lsphp binary built as well.
Installation of OLS web server and installation of PHP are separate processes.
I would recommend you might want to go through a couple of knowledge bases there and you might have all your answers there.
Feel free to ask if wikis are not clear or if you have more questions beyond wikis.