There are lots of threads on here about fist cameras. Have a look through the kit forum
Is it true that using a phone can act as a good camera for both videos and stills.
Not sure about video but for stills, yes it can.
I started using my Huawei P10 with a Velbon VTP787 tripod, a clamp mount to hold the phone and a remote. (All available from Amazon and under £25 for the lot.) The Huawei has a better camera than most phones and can be set to full manual so I can take long exposures in dark places like the one below. This was a pitch dark drain lit by torchlight and a 6 second exposure.
There are apps available for other phones to give you manual control