I guess freezes means stops. For a phone, this is likely just about identical to "lags".
I'd use "at times'. Seems fine to me.
I answer questions well, at times. Other times, well, not so well.
Not sure what you intend by "lags". It is ok, biut not obvious in meaning.
My phone goes slowly some times.
My phone camera resolution is not very high.
My phone camera is low resolution.
My phone camera is low-res.