Install specific version of package

If you want to install a specific version of a package, for example php7.2-phalcon, first run:

apt-cache policy php7.2-phalcon

This lists all the possible versions, for example:

Version table:
4.0.2-884+php7.2 500
4.0.0-861+php7.2 500
4.0.0-860+php7.2 500

Then run:
apt install php7.2-phalcon=4.0.0-860+php7.2

Which is basically:
apt install =