In the first screenshot provided above, you have a "Employer phone number txt" in the output schema. Click that and in the mapping field of query browser, press the function button. You will get a window open and select lookup_ext from the left window. Then do as i have shown in my screen shot. In the default column of lookup select the "Employer phone number txt" from target.
If the above looks hard for you another option is to insert an sql statement to update the column. Two ways to do it. Double click the target table and select the post load command. In the post load command insert the following -
update targettable set targettable.employeephoneno = lookuptable.employeephoneno from targettable innerjoin lookuptable on employeeid.targettable = employeeid.lookuptable.
The best practices is not to insert a post load command, instead add a script after the dataflow and insert a sql like this -
sql('datastorename','update targettable set targettable.employeephoneno = lookuptable.employeephoneno from targettable innerjoin lookuptable on employeeid.targettable = employeeid.lookuptable');
Arun