Gauntlet is good on Malphite but it really comes down to their team comp. The main issue is that FH is a damn good item on him as well but a lot of the stats overlap. For autoattacker comps or fed as fuck enemy ADCs I would get FH+Randuin's, gauntlet is better if other than the ADC they have ad casters rather than AD dps or if you need dps yourself. Of course you could get both but that would live you with little HP since it makes some obvious hp item choices for malph gold inefficient like kindlegem/SV due to CDR (you'll go over the cap) or Randuin's/Sunfire due to the extra armor that suffers from diminishing returns. But the latter is justified in some cases.
I dislike sunfire on him, it has some synergy with Abyssal but otherwise Randuin's is the better choice for Armor+HP as it allows you to do the niche malph excels at even better, making the enemy ADC fucking useless and quite likely dead as they cannot kite you or run away between Q and Randuin's (not to mention Gauntlet slow proc'd by E). It's not utter useless but Randuin's seems to be the superior choice unless they don't have any AD based dps at all. Really unless you don't need more armor than whatever the thing you build out of glacial provides you with Randuin's is the next best choice since you need that extra hp.
Trinity Force was always a solid choice on him if you needed to improve his DPS, only issue is that gauntlet cancels out sheen's passive (or the other way around). The good news is that you get glacial first anyway and later decide if you need the sheen. If you go FH you might as well go with TF, I would also argue that even despite losing out on the sheen passive component of TF it is still a very good damage item on him (AS synergizes with W, movespeed is great, phage slow is great, more hp is great). It is a luxury however, ult+combo+ignite murders the enemy ADC quite often, if your team can't mop up the enemy team when their adc is dead and you end up being the last man standing then you obviously need more damage. But most of the time the tanky items you build and CDR provided should be enough to do your job right and ensure victory in teamfights.
I also dislike abyssal and think visage is a better choice for mres, the aura is a nice bonus but if you need to build more mres than a basic negatron provides you don't need damage, you need survivability. Luxury item against magic damage-heavy teams (against which malph shouldn't really be picked).
Those are my two cents after playing a lot of malphite in eons past. But then again I haven't played in nearly half of a year IIRC, haven't read the changelog of patches since then and got demoted to Silver II so what do I know
