A cell phone (you call it a handphone) has a radio output power of up to 2W. When it is close to an unshielded electronic circuit then the circuit recifies the signal and produces high currents which can destroy it. A tiny piece of wire makes a good antenna at the microwaves frequencies from a cell phone.
Shielding a circuit from microwaves at 2W needs a certain education about the extremely high frequencies.
The circuit must be made on a pcb with a compact parts layout. A breadboard will cause all kinds of trouble.
The pcb must be installed in a metal case connected to 0V.
The mic must have shielded audio cable. Maybe the mic needs a shield around it.
The volume control must also be shielded.
The speakers might need to be shielded and use shielded audio cables.
Shielding a circuit from microwaves at 2W needs a certain education about the extremely high frequencies.
The circuit must be made on a pcb with a compact parts layout. A breadboard will cause all kinds of trouble.
The pcb must be installed in a metal case connected to 0V.
The mic must have shielded audio cable. Maybe the mic needs a shield around it.
The volume control must also be shielded.
The speakers might need to be shielded and use shielded audio cables.