Well, Poseidon's relationship with Zeus was a rocky one. There have been instances where Poseidon is jealous about Zeus' position as the King of gods. However, the same instance is said to be inspired by a conflict of interests, as Poseidon was not satisfied with Zeus' rule.
Poseidon took once part in a minor conspiracy in heaven; for he, along with Hera and Athena, had agreed to put Zeus in bonds. However, he was saved by Briareus (one of the HECATONCHEIRES), whom Achilles' mother Thetis had called to Zeus' rescue; and by just squatting down close to him and through the mere display of his force, Briareus frightened Poseidon and the goddesses away.
But, his views towards Zeus was not always filled with jealousy. There have been times when Poseidon helped Zeus with his troubles and also fought beside him.
He allied himself with Zeus in the battles against the Giants and repeatedly helped Zeus’s lovers. For example, he calmed the sea so Zeus, disguised as a bull, could cross it with Europa.
Source: Mythology 101: From Gods and Goddesses to Monsters and Mortals, Your Guide to Ancient Mythology
Looking into the case more deeply, Poseidon was not overly jealous of his younger brother and had a sense of respect towards him.
In Book Eight, Hera comes to Poseidon and asks him to join forces with her against Zeus, who is aiding the Trojans. His response displays the way in which his attitudes can change quickly. "But the Earth-Shaker growled at her in anger: 'Hera, mistress of babble that you are, what empty-headed talk is this? I would not dream of pitting all the rest of us against Lord Zeus. He overmasters all'" (188). Poseidon had recently attempted to dethrone Zeus on his own, but now became angered at Hera for even mentioning the idea. He switches his opinion again soon after this, however. In Book Thirteen, he chooses to disregard Zeus' orders to stay out of the combat and intervenes on behalf of the Achaeans. "Rancor within him deepened against Zeus… from the deep water, girdler of earth and shaker of earth, Poseidon came to arouse new spirit in the Argives" (300). He went from conspiring against Zeus, to anger at the mere mention of opposing Zeus, and back to opposing Zeus himself. Poseidon's attitudes towards Zeus here are not solid. Instead, they shift and sway, much like water does.
Source: A History of Poseidon by Robert James Reese, 2002
Further reading: http://www.maicar.com/GML/Poseidon.html