League of Legends (LoL) Question: Question about landing phase on top

It depends a bit on the matchup and team compositions, but at any rate you should ask for jungle help. "He's destroying me, come help or he'll take second turret" often convinces someone to come and help. The safest choice is to stay farming while taking your distance until someone comes to help, but you can also take a small risk and gank mid lane (or bot with Teleport) or steal from the enemy jungle.

If you do stay in lane, make sure to NOT ENGAGE before someone else comes, just play passive and ask for help. There's a chance your enemy laner started roaming or is invading your jungle, so make sure to roam too after clearing one or two waves if he/she disappears.

If you can roam or invade have in account a couple of things. First, if mid is pushed you won't be able to gank without diving, which could end up giving a free kill into a double if your top laner followed you. You should also have some form of CC, otherwise you'd probably be better off stealing the jungle. Now if you plan on invading the enemy jungle you have to make sure that either the jungler is in the bot side of the map or that you can kill him/her if he/she appears. I doubt you'd be able to do so if you're behind so just make sure that the enemy jungler is bot and try not to get caught by your top laner. Lastly, make sure to rotate top with your mid/jungler after a successful gank/invade, so that your enemy doesn't get to inhibitor tower because of your roam.

Basically, stay farming and mostly roam if your enemy is missing. Maybe you can roam by yourself but it's risky. Don't take the risk if the rest of your team is winning.

Pretty much EXACTLY what Ekki said. The important thing to remember is that you are behind and you cannot openly engage, but you can still defend your turret. Generally speaking, a lot of top laners are melee or have a short range on abilities, so they typically won't be able to safely harass you under your tower. The exception to this is a high dive potential champion such as Renekton or Pantheon. Even then it is possible to use their confidence in the dive against them, depending on who you are and what summs you have. Let me give some specific examples of good champs to play if you fear being dived when you get behind.

Jax is great at countering divers. His Counter Strike will literally cause them to waste their time when solo diving, not to mention you can usually kill them if they don't get away from your tower before taking the stun effect. Most people won't solo dive a Jax even if he's low, so it's a safe pick if you're uncomfortable laning against a diver.

Pantheon is a similar counter-dive champion, because of his Aegis of Zeonia. That said if you're behind enough as Pantheon that the enemy thinks he can dive you, you probably won't be much contribution to the team by yourself so as soon as the laning phase shows signs of ending, get with your team.

Vladimir is a solid pick top lane due to having range and his lack of being an Attack Damage based champion. His Sanguine Pool is great for preventing dives as it's a fairly long time frame to be untargetable and you can't be hit due to the untargetable effect.

Wukong is also a great choice for counter-diving because you can bait the enemy into diving while you pop Warrior Trickster and they'll be too low to attempt a second dive afterward in most cases, especially if you can land and E > AA > Q combo.

Renekton is amazing for countering dive attempts, especially if his Dominus is still able to be used. If someone dives a Renekton he can Dominus into a Ruthless Predator into an AA > Q combo and there's a good chance the enemy died under the tower by that point.

While I realize this isn't exactly what you asked, it's helpful information in case you play the above listed champions. But you should definitely go back to top, farm under tower, roam if your laner roams, and ask for help from the jungler. Also be sure to ward the jungle behind your tower in case the enemy jungler wants to dive with the enemy laner, because that can change things a bit.