The short answer is No.
The long answer:
The virtual column must be added through the code, there's no front-end interface to do that.
phpGrid only adds a "virtual" column that can be used for displaying aggregated value such as SUM based on existing columns. It does NOT change the database table structure for a good reason. Read on...
Adding a column essentially changes your database table structure, so it's not something you would want to do from the front-end by an user. It's something should be done by a very smaller number of people such as DBA, and ultimately through its back-end database administration program.