Can you help me to Get a SUM of a column $stock->entered_stock = Model_Admittance::select('SUM(`quantity`)')->where('phone','=',$admittance->phone)->get('quantity');
The ORM isn't really designed to run custom selects, it requires a mapping with the columns defined in the model, and the presence of the primary key in all results, to work.
There is experimental support for DB::expr() in selects in 1.8/develop, but yours will not work, as for a SUM() you will never have a primary key in the result.