This is the 3174th most frequent Russian word.
мобильных
"Mobile" or "of mobile" (genitive plural form).
Here, 'мобильных' is used as an adjective modifying the noun 'телефонов', indicating something (phones) that is mobile.
У меня есть зарядное устройство для мобильных телефонов.
I have a charger for mobile phones.
In this context, 'мобильных' is the descriptive adjective for 'устройств', referring to devices that are mobile or wireless.
В наше время мобильных устройств все больше.
Nowadays, there are more and more mobile devices.
Here, 'мобильных' qualifies 'приложений', describing applications designed for mobile use.