It looks like the 6.3-inch Samsung Galaxy Foneblet is more than just a rumor. In fact, it was supposedly hiding in plain sight at one point directly on Samsung's Support page. Additionally, even though the device is being called a Foneblet, it apparently will be properly classified as a tablet, despite having phone capabilities. Here's a quote from the guys at AndroidAuthroity with the full details,

Japanse site Ameblo has discovered the Fonblet hiding in plain sight, on the company’s download support page (see image below). However, we have not been able to replicate the search at this time.

The same source says the Fonblet will sport a 6.3-inch display, as initially rumored. The Galaxy Note 3 was also said to sport a 6.3-inch display, although more recent rumors claim that the third-generation Note will come with a smaller screen, at 5.9-inch.

When the Galaxy S4 was officially unveiled, we spotted an unexpected accessory for the handset that supports devices up to 6.3-inch displays, the Game Pad. Back then, it was believed that the Galaxy Note 3 will come in such a size, but it looks like the Fonblet may be the better candidate.

Despite being officially listed as a tablet on Samsung’s site, the Fonblet may sport phone capabilities too, since we’re looking at least at three different versions, all sporting cellular capabilities, as follows: GT-I9200 (GSM,) GT-I9205 (LTE/WCDMA) and GT-I9208 (TD-SCDMA/GSM) – of course, we’re yet to officially confirm that that’s the Foneblet’s family of model numbers, but this isn’t the first time we spotted that one of them, GT-I9205.
It's important to note that neither Android Authority nor our editors were able to replicate these search results. Furthermore, the source that shared this intel with them initially was the one who gave them the 6.3-inch display specs for this device as well. Because of this, we will lump this one in the rumor category, but it seems fairly solid.

Thanks to Astrix for the tip!

Source: AndroidAuthority