Explain the Node.js Event Loop phases in detail and how libuv facilitates them.

The Event Loop is a semi-infinite loop managed by libuv that offloads I/O operations to the system kernel or a thread pool, allowing Node.js to perform non-blocking I/O.

The event loop consists of several phases: 1. Timers (setTimeout, setInterval), 2. Pending Callbacks (I/O errors), 3. Idle/Prepare, 4. Poll (retrieving new I/O events), 5. Check (setImmediate), and 6. Close Callbacks. libuv provides the abstraction layer for these phases and manages a default thread pool of 4 threads for tasks like file I/O, DNS lookups, and crypto. Crucially, process.nextTick() and Promise microtasks are not part of libuv's loop but are processed between phases.