This is the 18190th most frequent Russian word.
часами
"For hours" or "for a long time."
'Часами' is used in this sentence to indicate the prolonged duration of talking on the phone.
Она часами разговаривала по телефону.
She talked on the phone for hours.
'Часами' expresses the long duration of walking in the park.
Мы гуляли по парку часами.
We walked in the park for hours.
'Часами' here highlights the extent of time spent playing the guitar, demonstrating endurance and enjoyment.