I use MAMP for local php development and recently needed to use php's pspell functions for a project. I found little help with this specific scenario (short of recompiling php, yuck) so this post explains how I got it done.
I am not positive but you may need xcode and xcode command line tools installed for this to work. This article might be helpful.
Install MacPorts if you don't have it already
Install aspell and the dictionary of your choice (I used "en"):
sudo port install aspell aspell-dict-en
note: for the next commands, you need to know the version of php you're running on MAMP. You can find this in the MAMP preferences under the PHP tab. For me it's 5.5.18
Download the php source for the version of php you are running, unarchive it, and move into the pspell source directory:
cd ~/Downloads/php-5.5.18/ext/pspell
Now (being sure to use the proper phpize binary for your php version) do:
/Applications/MAMP/bin/php/php5.5.18/bin/phpize
You should see something like:
Configuring for:
PHP Api Version: 20121113
Zend Module Api No: 20121212
Zend Extension Api No: 220121212
Next:
./configure --with-php-config=/Applications/MAMP/bin/php/php5.5.18/bin/php-config --with-pspell=/opt/local/
And finally, build the module file:
make
You should now have two files inside the ./modules/ directory: aspell.so and aspell.la - copy them into your php's extensions directory:
cp ./modules/* /Applications/MAMP/bin/php/php5.5.18/lib/php/extensions/no-debug-non-zts-20121212
Now add the extension to your configuration file in /Applications/MAMP/bin/php/php5.5.18/conf/php.ini
extension=pspell.so
Finally, restart your MAMP servers and (hopefully) you are good to go!