Homebrew/php has been deprecated.
As announced on the 19th of January this tap was archived on 31st March 2018.
All formulae were migrated to Homebrew/homebrew-core or deleted.
Find what existing PHP libraries you are using loaded through homebrew.
brew list | grep php
brew uninstall php56 php71 php71-intl etc
Remove leftover references to existing configurations.
If you skip this step, you may see errors down the road where php is referencing incorrect extension paths.
rm -rf /usr/local/etc/php/{7.0,7.1,5.6}
Install PHP from the new brew namespace
brew install php@7.1
Follow the instructions when that command is finished to add $PATH to your .bashrc or .zshrc
PHP extensions have been removed from brew, by default, most common extensions are already bundled, including intl and crypt.
Un[Fortunately] mongo was left out of the default. If you need it, go ahead and grab it using pecl.
pecl install mongodb
If you see this error, error fatal error: 'openssl/sha.h' file not found on installation after running pecl install mongodb
cd /usr/local/include
ln -s ../opt/openssl/include/openssl .