"what I understand from you reply that the php version is not necssary what shown by web, am I right?"
Yes. And you proved it ... your CLI test shows the earliest/oldest version of PHP available on server/service you currently have is 5.6 .. very old ... no longer supported.
"the current server can't be upgrade, according to the host support, so I can't upgrade the current Moodle site."
But you show that the range of PHP versions goes up to 8.3 ...
So it is possible to 'march' your 3.6/7 moodle upwards.
A march means upgrading the PHP version (via .htaccess file) to be able to run the higher version of Moodle - but not too high. In your server panel there might be a tool called 'EasyApache' ... which is kinda a mis-nomer because it has to do with the version of PHP a domain/site runs under + PHP extensions enabled.
Please study the chart:
http://www.syndrega.ch/blog/#php-and-dbms-compatibility-of-major-moodle-releases
You can upgrade the moodle to no higher than 3.7.
If you then set the PHP to 7.4 and upgrade the moodle to no higher than 3.10.x
Once upgraded and tested, make a full site backup ... code + DB + minimal moodledata/filedir/. Don't want to loose ground gained.
Next hop upwards within the range of PHP versions.
3.10.x to no higher moodle than 4.1.
Chart shows the low end of PHP to be 7.4.
What might help right now. Login to your moodle as site admin and go to Server -> Environment - update the component. Then in the drop down list of moodle versions select the next highest upwards. The screen will refresh. It will show greens/yellows/and reds. Reds must be addressed before the next hop upwards.
'SoS', Ken