yes and both no, it depends on what you want to do with the recording and how you want to deal with it. most phones are fitted with terrible audio support and likewise most amps are also fitted with less terrible but bad audio.
first you need to identify the right 3.5mm jack, it must be a proper mic out designed for mics only. I REPEAT, IT MUST BE A PROPER LINE OUT DESIGNED FOR MICS ONLY. if you bodoh go put a 3.5 adapter into a 6 cab out at 8 ohms..........you can say bye bye to your amp la.
then you need a 3 ring 3.5mm male to 2/1 ring 3.5mm male, this is the hardest and most important part. cause the amps run on 2 or 1 ring (it should be 1, mono) and different phone units run their rings differently. if i remembered correctly iphones has a special arrangement with their rings, so erm ya.
the reason you headache is cause the amp input is mono and often tends to be the top most ring on the jack, while the phone mic in, is the 3 third ring on the jack.
because phones are not designed (liek other audio equipment) for an independent mic in slot, you will play a guessing game to see if the phone can or cannot accept your line in.
this applies throughout other audio devices, ive encountered 3 ring jacks that dont work with other 3 ring jacks. so had to angle a bit.
so you got that headache to sort out, the next headache is the line out values vs your line in values. typically phones have very low line in impedance, its designed to power small mics that have almost no preamps.
the same cant be said of amps, some amps may have higher line out values to power small speakers, or to go into dedicated line in channels.
so you gotta worry about it and match it.
considering the mess, its rather wiser to connect teh amp 3.5 (LINE OUT) into a computer mic in slot cause that will work.
OR use a mic
Whole day searching male to male 3.5mm 3 rings jack, nothing. Than I remember I got an audio interface. It's a Focusrite 2i2. Can I connect the monitoring port(headphone sign) to 3.5mm handphone port?