Currently if you installed Debian 9 it will use FreeSWITCH 1.8 and if using Debian 8 it will use FreeSWITCH 1.6.
This has not been tested much with FusionPBX yet but it will likely work fine. It is still a good idea to do some of your own testing to certify its working well for everything you need. Or you can wait for others to do this and report back.
do you know about error about postegresql just after debian 8 or 9 installation script?
psql: could not connect to server: Connection refused
Is the server running on host "127.0.0.1" and accepting
TCP/IP connections on port 5432?
error: SQLSTATE  could not connect to server: Connection refused
Is the server running on host "localhost" (127.0.0.1) and accepting
TCP/IP connections on port 5432?<br/>
FusionPBX can be installed on several different operating systems. However, this guide assumes you are starting with a minimal install of Debian 9 with SSH enabled. This install has been designed to be fast, simple and modular, and generally takes 5 minutes or less. Installation times depend on factors like CPU, RAM, disk I/O and bandwidth.