A month is plenty of time for it to have healed (unless it was nearly severed...). I've had glass heal under the skin before, and it sounds like thar is what you most likely have. This really sux, because its sharp and transparent, and usually very small. It took months for me to finally dig it out on my own. It keeps doing damage, scar tissue pushes up and forms a bump, that tends to cause pain when you scrape it against something. Removing the bump helps for a while, but it reforms... Best to get a doctor to work on yours.
The phosphorus coating... hasn't killed you in a month, wouldn't worry about, it