Still spouting stuff like this are ya?"Is anti virus, such as AVG necessary for Android phones ? Is there any harm in installing it ,since it is free and doesn't cost anything ?"
No there is NO HARM in installing a virus protection on your phone! It´s necessary i would say!
Although I prefer Sophos Intercept X for Mobile from google play.
The app has consistently achieved a 100% protection score in AV-TEST’s comparison of the top Android security and antivirus apps.
It´s necessary especially since numerous annual reports tells the truth about mobile threats (like Kaspersky IT threat evolution reports to have found over 1.245 million malicious installers.. and that is only in Q2 this year! where close to 40.000 of these packages was mobile banking trojans: https://securelist.com/it-threat-evolution-q2-2020-mobile-statistics/98337/ )
Most often you hear about the Number of detected malicious installation packages, Q2 2019 – Q2 2020 always keep rising...
and an AV in your phone is necessary, especially since the number of EXPLOITS in the wild keeps growing.. This is the most dangerous thing your phone could run into since a properly run exploit will give the attacker ROOT or SYSTEM rights on your phone!
With this in mind I would say it´s quite careless to say it´s not needed... like some do...