SAN FRANCISCO — The bullpen phone rang in the eighth inning Wednesday afternoon. There was someone on the other end but nothing on the line.The San Francisco Giants trailed the St. Louis Cardinals by five runs. Rookie right-hander Trent Harris got the call to warm up. He reached for his glove. A deck swab would’ve been just as appropriate.In a six-batter span, everything changed. Brett Harris was hit by a two-out pitch. Turner Hill drew a walk to load the bases. Then Bryce Eldridge stepped to the plate and the crowd began to murmur. It was the kind of sound that fans make when they want to believe something good is about to happen. Eldridge is 21 years old. He’s already creating superstar expectations. He’s already fulfilling them, too.Eldridge shortened up, guided a two-run single through the left side and reacted with an imploring roar in the direction of his dugout. Then Jonah Cox blazed down the line while beating out an infield hit.The murmurs of hope grew into full-throated cheers and the inning got more interesting from there. Jung Hoo Lee started his at-bat with an automatic strike because of a pitch clock violation, he fouled off a pair of two-strike pitches, then he pulled a deep drive that struck the archway of the right-field arcade within arm’s length of the yellow stripe. The crowd let out an unfulfilled groan as umpire D.J. Reyburn signaled foul.That’s the kind of season it’s been in San Francisco. A rainout makeup in Atlanta notwithstanding, the Giants hadn’t swept a conventional series of at least three games all season. Their failures to finish one off included a pyrotechnic disaster on the last homestand against the Cincinnati Reds, when they blew a six-run lead in the ninth inning for the first time in franchise history. The Giants had been 0-6 when attempting to complete a three-game sweep and were well on their way to squandering another chance Wednesday after a series of misplays and mistakes awarded the Cardinals a comfortable lead.