Frequency response doesn't change noticeably with cables in normal conditions (exceptions are BA IEMs with very high resistance cable, or very low impedance phones).
But due to other attributes, perception of lows or highs seems to vary. You get thicker perception of lows with most copper cables, while highs seems to be enhanced when using silver or silver plated cables.
Audiosense T800 is a multi BA very low impedance (around 8-9ohms@1kHz) IEM.
Keeping low output impedance is critical for this IEM, if you want to get its normal frequency response (I don't know the impedance curve of T800, so I can't tell if you'll get harsher or tamed treble when using high output impedance).
Very few smartphones have output impedance below 1ohm, which is desirable in this case. I don't know output impedance of Samsung J3, I guess it's between 1 and 2 ohms (not bad).
In this case, the resistance of a decent cable won't affect much to total output impedance in proportion.
I get thicker bass perception while black background, so warmer perception overall, with cable 125, which has the lowest resistance in my list besides. But it's in the stiff and heavy side.
Cable 170/171 is my favorite copper, but you get more neutral perception. I'd choose any of these, 170/171 or 125, and would avoid silver or silver plated copper ones in your case.
Regardless of cable, to tame treble, I'd try tip rolling (narrow bore in long tip will help), ensure total output impedance below 1ohm (you'd need a different source), equalize, and/or add a bit of micropore tape in the nozzle.
