Using Tasksel and installing the lamp-server package still gives you php 5.3. Here's how to install a LAMP server with php 5.5.

Install php 5.5:

$ sudo apt-get update
$ sudo apt-get install -y python-software-properties
$ sudo add-apt-repository ppa:ondrej/php5
$ sudo apt-get update
$ sudo apt-get install -y php5

Install ApacheL

$ sudo apt-get install -y apache2
$ sudo apt-get install -y libapache2-mod-php5

Install MySQL:

$ sudo apt-get install -y mysql-server
$ sudo apt-get install -y php5-mysql

Bonus: Use PHP 5.4+ Webserver:

$ php -S localhost:8000