What is the ruling on fining someone who forgets their phone on in the mosque and causes disturbance to worshippers, with a charge of five Libyan Dinars to be used for the mosque's services, while exempting a stranger to the mosque?

Apologies for the delay in answering. The ruling on obligating someone who forgets their phone on to pay money depends on the ruling of discretionary punishment (ta'zir) with money. Most scholars prohibit discretionary punishment with money, and this is the madhhab of the four Imams. Those who permit it stipulate that it is for the ruler (wali al-amr), not for individuals. Therefore, it is not permissible to obligate the person to pay money, but if they wish to give charity of their own free will, they may do so.