The question arose concerning an individual who did not concentrate properly during the recitation of the Amida, and after reciting the words "Bi'mhera Be'yamenu" he did not know which Beracha he had been reciting. These words appear towards the end of two Berachot in the Amida – the Beracha of "Laminim Ve'lamalshinim," and the Beracha of "Tishkon Be'toch Yerushalayim." If a person cannot remember which Beracha he was reciting when he came to the words "Bi'mhera Be'yamenu," from which point in the Amida should he continue? Should he begin from the end of "Laminim," or from the end of "Tishkon Be'toch Yerushalayim"?
Some authorities claimed that a person in this case should continue from the Beracha of "Tishkon Be'toch Yerushalayim," in light of the famous Halachic principle of "Safek Berachot Le'hakel." This principle establishes that in any situation where one is uncertain as to whether a given Beracha is required, he should not recite the Beracha. Accordingly, some argued, in the case described above one should resume his recitation from the later Beracha, that of "Tishkon Be'toch Yerushalayim," rather than risk reciting the interim Berachot – "Laminim" and "Al Ha'sadikim" – unnecessarily.
Hacham Ovadia Yosef, however, in his work Yabia Omer (vol. 9, p. 207), disagrees. He notes that to the contrary, the principle of "Safek Berachot Le'hakel" dictates that one should return to the Beracha of "Laminim" in this case. If one continues reciting the Amida from "Tishkon Be'toch Yerushalayim," then he runs the risk of reciting an incomplete Amida. According to Halacha, one who skips even a single Beracha of the Amida is considered as though he has recited the Amida at all, and thus all the Berachot he recited as part of the incomplete Amida have been recited in vain. Hence, the individual in the aforementioned case should return to "Laminim," such that at worst he recites only two Berachot unnecessarily, rather than risk reciting an invalid Amida.
Summary: If during the Amida a person recites the words "Bi'mhera Be'yamenu" and cannot remember whether he was reciting the Beracha of "Laminim" or that of "Tishkon," he should assume that he had been reciting "Laminim" and continue the Amida from that Beracha.