What is the ruling on speaking with a boy over the phone if it is devoid of any arousal of desires or what one's soul inclines to?

There is no harm in a woman speaking with a boy who is not yet desired (i.e., not of an age of sexual attraction), because the Sharia (definition) has permitted her to speak with a man provided that Islamic etiquettes are observed. Allah Almighty says: "O wives of the Prophet, you are not like any other women. If you fear Allah, then do not be soft in speech [to men], lest he in whose heart is disease should covet, but speak with appropriate words." [Al-Ahzab: 32]. A woman is commanded to be firm in speech with non-mahram (definition) men, without raising her voice, and "appropriate words" refers to what is correct and not disapproved by the Sharia or by sound human nature.