BUY WITH CASH
Mycelium is a powerful android based Bitcoin wallet and decentralized exchange all in one.
The Local Trader part of the app allows you to find people near you that are selling Bitcoin for cash or other cryptocurrencies. If you wish to sell Bitcoin, then you can also list it through the app.
They have a reputation system, and your username is tied to a locally stored Bitcoin address. Mycelium won't let a seller list coins for sale if there is not enough Bitcoin in the connected address. Once you initiate a purchase from a listed seller, the app will launch an encrypted chat so the buyer and seller can coordinate the transaction.
You can find Mycelium's own step by step guide to Local Trader here.
Unfortunately Mycelium isn't currently available for iPhone. However, you can always purchase a Moto G or a Nexus 5 unlocked directly from Google, for $179 and $349, respectively. You don't even have to use it as an actual cell phone.If you plan on buying a large amount of coins, and don't want to change from the iPhone, then it could be worth it to just use the Moto G/Nexus 5 as a dedicated Bitcoin device using the WiFi.
Disclaimer: This post is intended solely to provide information. As I have no knowledge of individual circumstances and technical level, readers are expected to complete their own due diligence before proceeding with anything mentioned in this article. The topics discussed in this post are advanced and readers proceed at their own risk. Readers are expected to complete their own due diligence before purchasing or selling anything mentioned or recommended.