The PHP extension for the gRPC library Formula was removed
Last versions were
php55-grpc requires the following formulae to be installed:
autoconf 2.69 Automatic configure script builder

Recent formula history

Mike McQuaid Deprecate tap.
Stanley Cheung php-grpc 1.6.0
Stanley Cheung grpc: update to 1.3.2
Stanley Cheung php55-grpc: 1.1.0
Andy Blyler cleanup extension testing

Formula code at GitHub