The Silph Co. used to be a bustling skyscraper of activity but has since blocked all access to the building for visitors due to a faulty lift. Inside, you will only have access to the reception and one other room. In the reception, you'll find very few people but will encounter Steven Stone if you have met him in Vermilion City. He will give you one of the Hoenn starter Pokémon and, after beating Red, will offer you a trade.

Rotom Room
If you bring a Rotom to the elevator, it will take you to a special room where you can allow Rotom to enter one of the devices to allow it to change its form