PLEASE NOTE
PHP 7.3.6, and probably many previous versions, automatically sets SO_REUSEADDR when you use stream_socket_server().
php_network_bind_socket_to_local_addr() is called at https://github.com/php/php-src/blob/623911f993f39ebbe75abe2771fc89faf6b15b9b/main/streams/xp_socket.c#L675 and defined at https://github.com/php/php-src/blob/61a6a6ec51297506c54f3c6e60ace9b892d0a3e4/main/network.c#L401 and if you take a look you'll see
#ifdef SO_REUSEADDR
setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (char*)&sockoptval, sizeof(sockoptval));
#endif
I initially thought I'd need to play with context options to turn this on, but no, the simplest single-arg call with no error checking and just an address, works for me.
strace your PHP binary to be 100% sure:
...
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
...
The chances are you ARE using SO_REUSEADDR unless you're using a 100-year old UNIX clone in a month with a Z in it.