Simple you can call you controller from phtml like
Mage::getBaseUrl()/Modulename/Controllername/methodname
and to call Model
Mage::getModel('modulename/modelname')->methodname()
Example For controller
Mage::getBaseUrl()/priceconfig/index/checkcountryrate?price=$price
Where priceconfig
is my module-name and index
is my controller name and checkcountryrate
is my method
Example For Model
Mage::getModel('catalog/product')->load(1)
Please first read article about how magento MVC works then you can easily understand
Let me know if you have any query