Use the Rotom you caught in diamond, pearl and platinum.
You can't.
bring rotom and make sure he is first and go in the elevator and you will see rotom forms
In HeartGold and SoulSilver, you can access the 1st floor of Silph Co. as soon as you enter Saffron City however you can't go into the elevator in order to get to the 2nd floor unless you have a Rotom as your lead Pokemon.
Use the portals or the elevator.
Go up the elevator.
You can't.
bring rotom and make sure he is first and go in the elevator and you will see rotom forms
In HeartGold and SoulSilver, you can access the 1st floor of Silph Co. as soon as you enter Saffron City however you can't go into the elevator in order to get to the 2nd floor unless you have a Rotom as your lead Pokemon.
Use the portals or the elevator.
You need a rotom as the first Pokemon in your party and he will open the elevator 4 u. (Untested but have seen it irl (in real life)
Go up the elevator.
He is in Silph Co. but you need to trade rotom over from Pokemon platinum
Get a rotom
Get a Rotom and go in the elevator and Boom B1
there is no silph co in that game
In the Silph Co. building in HeartGold and SoulSilver, in order to gain access to the second floor, Steven Stone cannot be in the lobby and you also must have a Rotom be the lead Pokémon in your party.
You get the key card from inside the Silph Co. and head to the 5th floor via the elevator.