Phil's Reef is a patch reef on Agincourt Reef No. 3 that the Silverseries crew describe as having a spectacular array of corals, with huge plate corals providing perfect ambush grounds for groper. It is a compact site with a maximum depth around 16 m, which makes it easy to explore thoroughly in a single dive. The defining feature is the plate coral.

Great tiers of Acropora plates and tables spread out from the reef like shelves, some several metres across, creating shaded caves beneath. Large groper and coral trout use the shade to hide and ambush passing fish, and whitetip reef sharks often rest on the sand beneath the biggest plates. Hussar snapper, pink with a yellow stripe, school around the reef in loose groups.

On the sand margins blue-spotted lagoon rays lie half-buried and flick away as divers approach. Giant clams sit in the reef with mantles of electric blue, green and brown, and cuttlefish are common, hovering near coral heads and flashing colour changes. The coral top is shallow enough for snorkellers to see much of this, including the clams.

Because the reef is small and roughly circular, navigation is simple: you circle it deep, then circle it again shallow, keeping the reef on the same shoulder. The relaxed profile suits new divers and it is a good site for anyone wanting to practise buoyancy near fragile coral – the plates are easily broken, so keep fins well clear. Visibility usually runs 15 m or more.

For photographers the combination of layered plate coral and fish sheltering beneath makes excellent wide-angle compositions, and the cuttlefish and clams reward macro work. Phil's Reef is a gentle, rewarding dive and a nice contrast to the walls and drifts elsewhere on the Agincourt complex. Not to be confused with Phil's Backside, a deeper nearby site with sloping coral and bommies.

Agincourt day boats leave Crystalbrook Superyacht Marina (formerly the Reef Marina) on Wharf Street, Port Douglas, between about 8:00 and 8:30 am. Park in the marina car park or the free all-day street parking around Wharf and Dixie streets; Quicksilver, Poseidon and Calypso also run coach pick-ups from Port Douglas, Palm Cove and northern Cairns beaches. The run to the Agincourt ribbon reefs on the edge of the continental shelf is about 65–70 km north-east and takes roughly 75–90 minutes on the large catamarans (Silversonic is the fastest), longer on small-group boats such as Scuba IQ/Blue Dive.

You gear up on board and giant-stride from the dive deck at a permanent mooring; the skipper picks the sites on the day to suit wind and tide, so a named site is never guaranteed. Boats are back at the marina around 4:30 pm.

Agincourt is an outer ribbon reef on the shelf edge, so it is fully exposed to the south-east trade winds that blow from about April to September. Moorings on the protected western (back-reef) side remain diveable in 15–20 knots, but anything over 25 knots or a 2.5 m+ sea makes the crossing rough and operators may cancel or switch to more sheltered moorings. Calm spells in October–December give the glassiest days and 30 m+ visibility.

The wet season (December–April) brings northerlies, afternoon storms, cyclone risk and occasional reduced visibility after big rain events, although the outer reef is far less affected by run-off than inshore reefs. Marine stingers are present November–May. Tidal currents run along the reef edges and through the gaps between the Agincourt reefs; spring tides strengthen them, so exposed corners are usually dived on the neaps or near slack water.

Circle the patch reef at 10–14 m, peering under the large plate corals for groper and whitetips, then make a second, shallower lap at 5–8 m over the coral top looking for cuttlefish and clams. Safety stop on the reef top near the mooring.

Quicksilver Silversonic – daily, 3 dives across Agincourt 1–4; Poseidon (Quicksilver Group) – daily, 3 sites at Agincourt; Calypso Reef Cruises – regular Agincourt days; Scuba IQ / Blue Dive and Tech Dive Academy – small-group day trips several days a week.