The order of basicity in gaseous phase for amines with the same alkyl group is:
In the gaseous phase, basicity increases with more alkyl groups due to electron donation: tertiary > secondary > primary, as per the PDF’s basicity section.
Ref: NCERT Class 12 Chemistry > Chapter 13: Amines > Topic: Reaction with Nitrous Acid and Diazonium Salts - Part 1