install the PHP version you want on Raspbian. Tested with 5.5 and 5.6. It may work for PHP 7.x, too.

install_latest_php_raspberrypi.sh

#!/bin/bash

# credits: http://stackoverflow.com/questions/31280912/how-to-install-php-5-6-on-raspbian-wheezy

### VARIABLES ###

# type here the specific php 5.x version you want to install
PHP_VERSION="5.6.27"

### SCRIPT ###

# check if script is running as root
if [[ $EUID -ne 0 ]]; then
    echo "Sorry, you have to be root."
    echo "Try again using sudo"
    exit 1
else
    echo "Running as root..."
fi

# getting real number of cores
# CORES=$(cat /proc/cpuinfo | grep Hardware | wc -l)

# Check PHP version before start
# latest version in repo should be 5.4, which is no longer supported.
echo "Currently installed PHP version is..."
php -v

# working in temporary dir
mkdir -p /tmp/php_install
cd /tmp/php_install

# Get the PHP source
# You can find the latest version number on the PHP download page: http://php.net/downloads.php
# Change `nl1` to your nearest mirror. Find the mirror list here: http://php.net/mirrors.php.
wget http://nl1.php.net/distributions/php-$PHP_VERSION.tar.bz2

# Unpack
tar -xvjf php-$PHP_VERSION.tar.bz2

cd php-$PHP_VERSION

apt-get update
apt-get install libxml2-dev
./configure

# getting cpu architecture
RPI_HW=$(cat /proc/cpuinfo | grep Hardware | awk '{print $3}' | head -1)

if [ "$RPI_HW" = "BCM2709" ]; then
    # if on RPi 2 or RPi 3 use 4 cores.
    make -j4
else
    # if on RPi 1 or unrecognized cpu (future Pis?) use 1 core
    make
fi

make install

# Check PHP version
echo "now printing the newly installed PHP version..."
php -v