PHP Version 7.1 Formula was removed
Last versions were

Revision: 25

php71 requires the following formulae to be installed:
enchant 2.2.3 Spellchecker wrapping library
freetype 2.9 Software library to render fonts
gettext GNU internationalization (i18n) and localization (l10n) library
gmp 6.1.2_2 GNU multiple precision arithmetic library
icu4c 61.1 C/C++ and Java libraries for Unicode and globalization
jpeg 9c Image manipulation library
webp 1.0.0 Image format providing lossless and lossy compression for web images
libpng 1.6.34 Library for manipulating PNG images
libxml2 2.9.7 GNOME XML library
unixodbc 2.3.6 ODBC 3 connectivity for UNIX
readline 7.0.3_1 Library for command-line editing
openssl 1.0.2o_1 SSL/TLS cryptography library
postgresql 10.3 Object-relational database system
httpd 2.4.33 Apache HTTP server

Recent formula history

Kevin Abel php71: migrate to homebrew/core (#4798)
Sean Molenaar php71 7.1.14
Sean Molenaar php71: 7.1.13
Andreas Braun php71 7.1.12
Andreas Braun php71 7.1.11

Formula code at GitHub