Ok, got it work.

Directory structure, there seems to be problem with location of you php.conf file. My dir structure is:

root@hi /home/test/stackoverflow_79617562 $ ls -laR
.:
total 20
drwxr-xr-x 4 root   root   4096 May 12 16:25 ./
drwxr-x--- 9 jjakes jjakes 4096 May 12 16:01 ../
-rw-r--r-- 1 root   root    342 May 12 16:23 docker-compose.yml
drwxr-xr-x 3 root   root   4096 May 12 16:29 nginx/
drwxr-xr-x 2 root   root   4096 May 12 16:29 src/

./nginx:
total 12
drwxr-xr-x 3 root root 4096 May 12 16:29 ./
drwxr-xr-x 4 root root 4096 May 12 16:25 ../
drwxr-xr-x 2 root root 4096 May 12 16:29 conf.d/

./nginx/conf.d:
total 12
drwxr-xr-x 2 root root 4096 May 12 16:29 ./
drwxr-xr-x 3 root root 4096 May 12 16:29 ../
-rw-r--r-- 1 root root  491 May 12 16:23 php.conf

./src:
total 12
drwxr-xr-x 2 root root 4096 May 12 16:29 ./
drwxr-xr-x 4 root root 4096 May 12 16:25 ../
-rwxrwxrwx 1 root root   20 May 12 16:29 index.php*

so try moving your php conf to ./nginx/conf.d/php.conf file.