biber, two issues

[Karl Berry]

    1. if I try >>> /usr/local/texlive/2018/bin/x86_64-linux/biber --help

How about 2019? (Probably no better, but may as well try.)
You can download just that one binary without anything else from
https://sourceforge.net/projects/biblatex-biber/files/biblatex-biber/current/binaries/Linux/
(among other places).

    Unicode::Collate object version 1.25 does not match bootstrap
    parameter 1.21 at /loader/HASH(0x2221ce0)/DynaLoader.pm line 210.

Biber is distributed unusually -- as a self-unpacking binary which
includes all the myriad Perl packages it depends on, many of which need
compilation.  I surmise something on your system is too old to get
through that process (it doesn't work on my centos7, either), but that's
just my guess.

The best way I know of to report the problem to the biber maintainer
(Phil Kime) is to open a bug:
https://sourceforge.net/p/biblatex-biber/bugs/
(You can also find his email address on the web without too much
trouble, but I don't want to post it here.)

    In the latter case, files are owned by user apache, and I suspect
    that biber does not like that.  How do I fix it?

What matters is not the owner of the files as such, but whether the
user/group which Apache is running on (apache:apache, probably) has
permission to write the directories. Biber might try to write in some
temporary directory which apache cannot write to, but again, that's just
a guess. The error_log for your localhost web server would hopefully
have error messages about the actual problem. Maybe the PHP stuff also
plays into it. (If you change your script to write debugging messages to
standard error, they should also show up in the error_log.)

Good luck,
Karl